Sensation and Perception
Sensation: the conversion of energy from the environment
into a pattern of response by the nervous system.
Perception: the interpretation of sensory information.
I. Sensing the World Around Us
A. Stimuli: energies in the environment that affect what we do.
B. Receptors: the specialized cells in our bodies that convert
environmental energies into signals for the nervous system.
1) Cones: are utilized in color vision, daytime vision, and
detail vision and are most plentiful around the center of the
2) Rods: are adapted for vision in dim light and are most
plentiful in the periphery of the retina.
D. Fovea: the center of the human retina, and the location of
the highest proportion of cones.
II. The Detection of Light
A. Light: the stimuli that the visual system is designed to detect.
B. Visible Light: a small portion of the electromagnetic spectrum,
which is the continuum of all the frequencies of radiated energy.
III. The Structure of the Eye
IV. Common Disorders of Vision
A. Myopia (nearsightedness): the person can focus well on
nearby objects, but not distant ones.
B. Hyperopia (farsightedness): the person can focus well on
distant objects, but not on nearby ones.
C. Glaucoma: increased pressure within the eyeball, causing
damage to the optic nerve and loss of peripheral vision.
D. Cataract: the lens of the eye becomes cloudy.
V. Dark Adaptation:
in the ability to see
in dim light.
VI. Color Vision
A. The Trichromatic Theory: our receptors respond to three
1) Short wavelengths are seen as blue.
2) Medium wavelengths are seen as green.
3) Long wavelengths are seen as red.
B. The Opponent-Process Theory: we perceive color not
in terms of separate categories, but rather in a system of
1) Red vs. Green
2) Yellow vs. Blue
3) White vs. Black
C. The Retinex Theory…
1) Color Constancy: the tendency of an object to appear
nearly the same color even though we see it in a variety of
1) About 4% of all people are partly colorblind
(8% of men, “1 out of 12”, and 1% of women).
2) Red-green colorblindness is the most common type.
3) Yellow-blue colorblindness is very rare.
4) Complete colorblindness is extremely rare.
VII. Perceiving the World Around Us
A. The Perception of Minimal Stimuli
B. Subliminal Perception: is the idea that a stimulus can
influence behavior even when it is so weak or brief that
we do not perceive it consciously.
1) Subliminal: below the sensory threshold.
2) Supraliminal: subtle, or faint, but still processed
C. What subliminal perception CANNOT do…
1) Subliminal stimuli in advertisements…
2) Messages in music…
3) Subliminal audiotapes…
D. What subliminal perception CAN do…
VIII. Recognition of Patterns and Contrast
A. Face Recognition
B. Size Contrast
C. Brightness Contrast: how the apparent brightness of an
object that you are looking at can be increased or decreased
by the objects around it.
IX. The Feature-Detector Approach
A. Feature Detectors: specialized neurons that respond to the
presence of certain simple features, such as angles and lines.
1) The Waterfall Illusion
2) BUT, feature detectors can’t explain…
X. Gestalt Psychology: focuses on the human
ability to perceive overall patterns.
A. Visual Perception: is an active creation, not merely the
adding up of lines and movement.
1) Figure and Ground: what’s the object of focus and what’s
2) Reversible Figure:
a stimulus that can be
perceived in more than
B. Gestalt Principles…
1) The principle of proximity: states that we perceive
objects close together as belonging to a group.
2) The principle of similarity: states that we perceive
objects that resemble each other as forming a group.
3) The principle of good continuation: states that we
perceive lines as continuous even when they are interrupted.
4) The principle of closure: states that we fill in gaps in
lines, or close familiar figures.
5) The principle of common fate: states that we group
together objects that appear to be moving in the same
XI. Perception of Movement and Depth
A. Visual Constancy: our tendency to perceive objects as
keeping their size, shape and color even though the
image that strikes our retina changes from moment to
B. Distal Stimulus: the actual physical object in the world.
C. Proximal Stimulus: the optical image on the retina of the
physical object in the world.
D. Shape and Size Constancy…
E. Vestibular System: works to keep the visual system
informed of the movements of your head.
F. Induced Movement: a visual illusion in which we incorrectly
perceive the object as moving.
G. Stroboscopic Movement: an illusion of movement created
by a rapid succession of stationary images.
H. Phi Effect: in which your brain creates motion from rows of
adjacent lights blinking on and off sequentially.
I. Monocular Cues: needing only one eye.
1) Object Size: the same sized object produces a larger image
on the retina when it is closer than when it is further away.
2) Detail: objects that are closer can be seen in greater detail
than when they are farther away.
3) Interposition: nearby objects will obstruct objects that are
4) Texture Gradient: clusters of objects will seem more
densely packed the farther away the clusters are.
5) Shadows: give clues to distance depending on size and
6) Motion Parallax: close objects will pass by faster than
J. Binocular Cues: depending on both eyes.
1) Retinal Disparity: is the difference in apparent position of
an object seen by each retina.
2) Convergence: the degree to which our eyes must turn in
to allow us to focus on a very close object.
XII. Optical Illusions: misinterpretations of
A. The Moon Illusion